Semiconductor device package and method of manufacture

ABSTRACT

A structure and method to improve saw singulation quality and wettability of integrated circuit packages ( 140 ) assembled with lead frames ( 112 ) having half-etched recesses ( 134 ) in leads. A method of manufacturing lead frames includes providing a lead frame strip ( 110 ) having a plurality of lead frames. Each of the lead frames includes a depression ( 130 ) that is at least partially filled with a material ( 400 ) prior to singulating the lead frame strip.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of prior U.S. application Ser. No.13/537,392, filed Jun. 29, 2012, now U.S. Pat. No. 8,841,758. The entiredisclosure of U.S. application Ser. No. 13/537,392 is herebyincorporated by reference herein.

BACKGROUND

This invention relates generally to semiconductor device packages, andmore specifically to leads of flat-pack no-lead semiconductor devicepackages.

RELATED ART

A semiconductor device may be mounted on a lead frame and encapsulatedin a semiconductor device package (hereinafter “package”). A packageutilizes leads for externally providing and receiving signals and power.One type of package is a flat-pack no-lead package where the leads areexposed at a bottom and at a side of the package.

A lead frame strip (hereinafter “strip”) is populated with multiple leadframes. An encapsulating mold compound and portions of the strip betweenlead frames are cut during singulation of the strip to create individualpackages.

One type of wettable flank of a lead of a flat-pack no-lead packageincludes a cavity, or recess, on the end of the lead, which has beenplated, such as with matte tin, nickel palladium gold or palladium, sothat solder can wet to the recess. Flat-pack no-lead packages withwettable flanks have better solder fillet formation and allow for easiervisual inspection of a solder joint after surface mounting of thepackage on a printed circuit board (hereinafter “PCB”). Aftersingulation, a recess of a wettable flank appears as a volume of metalmissing from a central area of a bottom, external corner of a lead. Arecess is narrower than a lead so as to prevent the mold compound fromfilling the recess. The wettable flank produces a wettable surface thatis higher than a bottom of the package. A fillet is an extension of thesolder joint at a side of a package that can be visually inspected. Thewettable flank facilitates formation of a fillet. Surface tension causesthe solder to wet up into the recess of the wettable flank, and thesolder may advantageously form a fillet.

Typically, two recesses are formed from a depression in a strip. Theprocess of forming a depression is part of a process of forming the leadframes of a strip and is typically done by a lead frame manufacturer.The depression can be created by a partial-etch, or half-etch, processduring manufacture of the lead frames. One known depression is shaped asan elongated slot on a bottom surface of a lead of one lead frame and ona bottom surface of a lead of an adjacent lead frame and on a bottomsurface of an intermediate portion of the strip between the adjacentlead frames.

Saw singulation cuts through portions of the strip between lead frames.The cutting process removes, as swarf, much of the intermediate portionof the strip including a middle portion of the depression. End portionsof the depression, which remain after saw singulation, become therecesses of the wettable flanks. Most leads are copper. During sawsingulation, copper may, due to a ductile nature of copper,disadvantageously fill a portion of the depression that becomes (aftersingulation) the recess of a wettable flank. The copper may peel when ablade of a saw arrives at an edge of a depression and copper debris mayadhere to the edge of the depression. As a result, the copper debris mayreduce at least one of the dimensions of the recess. Such reduction inthe at least one dimension of the recess is most apparent when therecess was small prior to saw singulation. The lead frame is unsupportedat the depression, and, as a result, when the strip is saw singulated,burrs or tear-outs of copper may form, and the depression may captureother saw debris, such as epoxy, from the mold compound. Such copper andother saw debris in the recess of a wettable flank can result in avisual rejection of a package. Also, such copper and other saw debris inthe recess of a wettable flank can result in an increased risk of adefect in a solder joint formed during surface mounting of the packageto a PCB because such debris may detrimentally affect solder jointformation. Additionally, the debris may fall out of the recess and on tothe PCB.

When the pitch is less than 1 mm, one known method to avoid the debristhat may form in recesses of wettable flanks during saw singulation isto punch singulate, rather than to saw singulate, flat-pack no-leadpackages. However, punch singulation is disadvantageous because a numberof individual units on a strip when a strip is to be punch singulatedcannot be as large as a number of individual units on a strip when thestrip is to be saw singulated.

Another known method reduces a rate of sawing and/or uses specializedblades in an attempt to reduce accumulation and retention of debris inrecesses; however, such known methods do not eliminate accumulation andretention of debris in recesses.

Another known method uses a structure that includes a through holeopening in a lead, and then fills the through hole opening with solderprior to singulation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited by the accompanying figures, in which like references indicatesimilar elements. Elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale.

FIG. 1 is a bottom plan view of a portion of a strip including portionsof two lead frames, showing depressions in the lead frames.

FIG. 2 is a cross-sectional taken along line 2-2 of FIG. 1.

FIG. 3 is a cross-sectional taken along line 3-3 of FIG. 1.

FIG. 4 is a bottom plan view of a portion of the strip of FIG. 1 aftermaterial has been placed into depressions in accordance with variousembodiments of the invention.

FIG. 5 is a cross-sectional taken along cut-line 5-5 of FIG. 4 showing across-section of a depression with the material in the depression.

FIG. 6 is a cross-sectional taken along cut-line 6-6 of FIG. 4 showing across-section of a depression with the material in the depression.

FIG. 7 is a top isometric view of a package produced from a stripsimilar to the strip of FIG. 1 when the material in the depressions is awettable material that is present in depressions during singulation andremains in a recess at an external corner of each lead aftersingulation, and showing the wettable material in the recess of theexternal corner of each lead, in accordance with various embodiments ofthe invention.

FIG. 8 is a bottom plan view of the semiconductor package of FIG. 7.

FIG. 9 is a perspective view of an enlargement of an encircled regionshown in FIG. 8 showing several recesses and showing the wettablematerial in the recesses.

FIG. 10 is a perspective view of an enlargement of an encircled regionshown in FIG. 9 showing one recess and showing the wettable material inthe recess.

FIG. 11 is a partial, side-elevational view illustrating the manner inwhich the package of FIGS. 7-10 is mounted to a PCB, and showing afillet.

FIG. 12 is a top isometric view of a package produced from a stripsimilar to the strip of FIG. 1 when the material in the depressions is aremovable material that is present in the depressions during singulationand is removed after singulation, and showing a debris-free recess at anexternal corner of each lead after the removable material is removed, inaccordance with various embodiments of the invention.

FIG. 13 is a bottom plan view of the package of FIG. 12.

FIG. 14 is a perspective view of an enlargement of an encircled regionshown in FIG. 13 showing several debris-free recesses in accordance withthe invention.

FIG. 15 is a perspective view of an enlargement of an encircled regionshown in FIG. 14 showing one debris-free recess in accordance with theinvention.

FIG. 16 is a perspective view of an enlargement of a prior art recessshowing debris in the prior art recess.

FIG. 17 is a partial, side-elevational view illustration the manner inwhich a prior art package that includes the prior art recess of FIG. 16is mounted to a PCB and shows how formation of a fillet is adverselyaffected by debris in the prior art recess.

FIG. 18 is a flow diagram of a method of assembling a flat-pack no-leadpackage in accordance with one embodiment of the invention.

FIG. 19 is a flow diagram of a method of assembling a flat-pack no-leadpackage in accordance with another embodiment of the invention.

FIG. 20 is plan view of a strip, given by way of example, which may beused in one or more methods of assembling packages in accordance withvarious embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 is a bottom plan view of a portion of a dual, flat-pack no-leadtype strip 110 including portions of two adjacent lead frames 112,showing depressions 130 in each lead frame 112. Filling the depressions130 in each lead frame with an appropriate material prior to sawsingulation prevents formation and accumulation of debris withinrecesses of wettable flanks of the leads of each flat-pack no-leadpackage produced from the strip 110, thereby facilitating sawsingulation and/or allowing a wider process window for saw singulation.The methods in accordance with the invention prevent accumulation ofdebris in the recesses during assembly of QFN-style packages. Performingsaw singulation when material is in the depressions 130 prevents theformation of copper burrs in the recesses.

FIG. 2 is a cross-sectional taken along line 2-2 of the strip 110. Eachlead 120 has a bottom surface 128 and a top surface 226.

FIG. 3 is a cross-sectional taken along line 3-3 of the strip 110.

FIG. 4 is a bottom plan view of the portion of the strip 110 with amaterial 400 disposed in the depressions 130.

FIG. 5 is a cross-sectional taken along cut-line 5-5 of the strip 110showing a cross-section of a depression 130 with the material 400 in thedepression.

FIG. 6 is a cross-sectional taken along cut-line 6-6 of the strip 110showing a cross-section of a depression 130 with the material 400 in thedepression. The material 400 is represented by cross hatching in thedepressions 130 of FIGS. 4, 5 and 6. As explained more fullyhereinbelow, the material 400 is one of a solder wettable material(hereinafter “wettable material”) 200 and a removable material 300.

Each lead frame 112 of the strip 110 includes an outer frame structure114 that surrounds a centrally positioned opening 116 into which themold compound, shown diagonally hatched, penetrates duringencapsulation. The lead frame 112 may include a die pad 118 disposedwithin the opening 116. The successive lead frames 112 of the strip 110may extend in a two dimensional matrix presenting rows and columns oflead frames. Each lead frame 112 further comprises sets of leads 120disposed side by side at intervals along respective sides of each leadframe 112 and separated from adjacent lead frames by a gap G.

Before encapsulation, semiconductor dies (not shown) are mounted on andattached to respective lead frames 112. Electrical connections are madebetween bonding pads (not shown) on the die and respective ones of theleads 120 using wires. The lead frames 112 are then encapsulated byapplying the mold compound to the strip 110, either to the entire strip,or to form individual moldings for individual packages.

Before singulation, as shown in FIGS. 1 and 4, the leads 120 areintegrally connected to, and supported by, the outer frame structure 114and extend inward into the opening 116 toward the peripheral edge of thedie pad 118. In each strip 110, the outer frame structure 114 includesan intermediate common bar 132, which are common to adjacent lead frames112. The outer frame structure 114, including the common bar 132, is cutaway and discarded during singulation.

As shown in FIGS. 1 and 4, the depressions 130 of the leads 120 ofadjacent lead frames 112 within the same column or row, may be formed bysemi-etching or partial-etching, which is etching the material of thestrip 110 part-way through its thickness. The partial-etching formspartially-etched, elongated depressions 130 extending across the commonbar 132 of the outer frame structure 114 common to adjacent lead frames,so that the opposite end portions of the depressions 130 later form(after singulation) recesses 134 at the ends of the juxtaposed leads 120of the adjacent lead frames.

A saw street S of the strip 110 extends along the common bar 132. Thepassage of a saw blade along each saw street S separates the adjacentlead frames 112 from each other. Orthogonal row and column saw streets Sextend within a two-dimensional strip 110. A width of a blade used inthe saw singulation process is such that the saw street S does notinclude the opposed end portions of each depression 130.

Typically, the saw blade is the same width as each of the saw streets Sand straddles the common bar 132 of the outer frame structure 114 whileit is sawing. Thus, during the saw singulation process, the saw bladecuts along each saw street S longitudinally, cutting into and along thecommon bar 132 of each outer frame structure 114, which reduces all themetal material of the common bar 132 to swarf, which is discarded, andfurther removes or severs a portion of each of the leads 120 to formtheir outer ends at the peripheral edge surfaces of the package 140, inaddition to cutting the mold compound. The saw singulation process alsocuts away the middle portion of depressions 130.

FIG. 7 is a top isometric view of a completed quad, flat-pack no-leadpackage 140 when the material 400 in the partially-etched depressions130 is the wettable material 200, which was present in thepartially-etched depressions during singulation. The package 140illustrated in FIG. 7 was manufactured, or assembled, utilizing a firstmethod (see FIG. 18) in accordance with one embodiment of the invention.FIG. 7 shows the wettable material 200 in the recess of the externalcorner of each lead 120 of the package 140.

FIG. 8 is a bottom plan view of the package 140. The wettable material200 is represented as a small solid dark area in each recess of FIGS. 7and 8.

FIG. 9 is a perspective view of an enlargement of an encircled regionshown in FIG. 8 showing several recesses 134 and showing the wettablematerial 200 in the recesses as cross-hatching.

FIG. 10 is a perspective view of an enlargement of an encircled regionshown in FIG. 9 showing one recess 134 and showing the wettable material200 in the recess as cross-hatching.

The package 140 includes a package body (hereinafter “body”) 142 formedby the hardening of electrically insulating plastic encapsulationmaterial, or mold compound, which is applied to a strip such as thestrip 110. Each package 140 comprises sets of discrete, electricalcontact elements or leads 120 disposed side by side at intervals alongrespective sides of the bottom face 146 of the package and extendingperpendicularly to the side of the corresponding bottom face 146. Inpackage 140, sets of leads 120 are disposed on all four sides of thebottom face 146 and are exposed at the bottom face 146 and at the sideedges 150 of the package for soldering to the electrical connections ofthe support. In a dual no-lead package (not shown), sets of leads 120are disposed on only two opposed sides of the bottom face 146. As shownin FIGS. 7-10, the ends of the leads 120 of the package 140 terminateapproximately flush with the sides of the singulated, completed package.

The saw singulation process separates the packages 140 from each otherby cutting and separating both the individual lead frames 112 of thestrip 110 and the plastic encapsulation material in a manner completingthe formation of the body 142 of each package 140. The completely formedpackage 140 defines a top face 144 and an opposing bottom face 146,which are generally rectangular. A side edge 150 extends transversely tothe top face 144 and bottom face 146 of the body 142.

The leads are exposed within the bottom face 146 of the body 142. Theouter ends of the leads 120 are exposed within the side edges 150 of thebody 142. The leads have recesses 134 formed at a corner of each lead120 formed by the bottom surface 128 of each lead and the exposed outerend of each lead 120 of a package 140. The bottom surface 128 of eachlead near this corner functions as an electrical contact portion of eachlead. Completion of the saw singulation process results in a recess 134being formed within each lead 120. Each recess 134 is formed in a cornerregion of the corresponding lead 120 defined by an outer end and thebottom surface 128 thereof. The recess 134 is disposed within the bottomsurface 128 and the outer end, but does not extend to the top surface226 or either of the side surfaces. Each recess 134 has a generallyconcave configuration. During solder mounting of the package 140 on aPCB 152 (see FIG. 11), solder can reflow up into the recesses 134. Theelectrical contact surface portions and outer end, including therecesses 134, of each lead 120 (which are exposed outside of the body142) may have a plating layer applied to facilitate soldering to the PCB152.

The methods in accordance with the invention overcome the problem ofburrs and debris collecting in the recess 134 during saw singulation ofpackages 140. The methods in accordance with the invention filldepressions 130 with either the wettable material 200 or with theremovable material 300. The removable material 300 does not compromisethe wettability of the lead 120 or of the recess 134. The removablematerial 300 has one of rigid and semi-rigid properties when singulationis performed; however, the removable material may be fluidic when it isplaced in the depressions 130. A depression 130 that is at leastpartially filled with material 400 at time of singulation eliminates (orat least effectively eliminates) debris that would otherwise accumulatein the recesses 134 as a result of singulation, especially sawsingulation. Much of the debris that accumulates in the recesses 134 asa result of using known methods of singulation may disadvantageouslyremain in the recesses indefinitely. The methods in accordance with theinvention improve the ability to produce a debris-free recess 134 inpackages 140 with fine pitch leads 120 by preventing accumulation ofdebris in the recess during assembly of the package. The methods inaccordance with the invention increases a likelihood of forming aninspectable solder joint after mounting on the PCB 152. The methods inaccordance with the invention fill the depression 130 with a material400 that is solid enough to prevent formation of burrs, or tear-outs,during, and as a result of, saw singulation.

A first method in accordance with the invention fills the depressions130 prior to singulation with the wettable material 200, which preventsformation and accumulation of burrs and debris during singulation, anddoes not require removal. With the first method, the depression 130 isat least partially filled with the wettable material 200 such as solder,which is typically tin alloyed with copper, lead, silver or bismuth. Invarious embodiments, the wettable material 200 is solder, solder paste,tin, bismuth, indium, gold, silver, another wettable material, orcombinations thereof. In one embodiment, the solder is SAC305 or SAC405,where S=tin, A=silver and C=copper. For example, SAC305 is 96.5% tin, 3%silver, and 0.5% copper. The depressions 130 may be filled with thewettable material 200 in several ways. The first method fills thedepression 130 with the wettable material 200 by squeegee application,stencil print or screen print to move solder paste into the depressions130, then reflows the wettable material prior to continuing with normalassembly of the package 140. In another embodiment, a solder jet is usedwhich streams solder paste through a small nozzle to fill thedepressions 130. In another embodiment, solder paste that has beenatomized into nanoparticles is sprayed into the depressions 130. Inanother embodiment, solder balls are placed into each depression 130.The solder balls are then melted or reflowed to fill the depressions130. In another embodiment, the strip 110 is masked such that only thedepressions 130 are exposed, wherein the wettable material 200 is formedin the openings of a mask. In another embodiment, the strip 110 isplated with the wettable material 200 until the depressions 130 becomefilled. In some embodiments of the first method, the wettable material200 that is placed in the depressions 130 is then heated to reflow thewettable material. In each embodiment of the first method, the strip 110is singulated after the wettable material 200 is placed in thedepressions 130. In each embodiment of the first method, the wettablematerial 200 is not removed after it is placed in the depressions 130.Maintaining the wettable material 200 in the depression 130 aftersingulation prevents any further accumulation of debris in the recess134 after singulation.

A second method in accordance with the invention fills the depression130 prior to singulation with a removable material 300 that can be hardenough to prevent the burrs and debris from collecting in the recess134, and that is easily removable using water or other chemistry commonto semiconductor processing (such as photo resist). In one embodiment,the removable material 300 one of a hot-water soluble adhesive, ahot-water soluble thermoplastic material and a hot-water solublethermosetting polymer material. The hot-water soluble material isapplied at a high enough temperature (about 100° C.) for the material tobe in a liquid form. The hot-water soluble material is adequately solidwhen cured, but, after it has cured, it rinses cleanly away in hotwater. An example of such a hot-water soluble material that can be usedis AquaBond® ABS-65 (AquaBond is a trademark of AquaBond Technologies,Inc., of Camarillo, Calif.). In one embodiment, the strip 110 is putinto in a bath of the hot-water soluble material at a high enoughtemperature (about 100° C.) for the material to be in a liquid form. Inanother embodiment, the hot-water soluble material is heated to a highenough temperature (about 100° C.) for the material to be in a liquidform, and it is applied to the strip 110 by screen printing using astencil. Then, the hot-water soluble removable material 300 on the strip110 is allowed to return to room temperature, and the hot-water solubleremovable material hardens or solidifies, and it becomes at leastsemi-rigid. The recesses 134 remain filled with the hot-water solubleremovable material 300 during singulation, which prevents debris fromentering the recess 134 during the saw singulation process. Next, thepartially singulated strip or the individual units are put into ahot-water bath to remove the hot-water soluble removable material 300from the recess 134. An exposed debris-free recess 134 results. In oneembodiment, the partially singulated strip or the individual units areimmersed in hot water or sprayed with hot water (at about 80-90° C.)until the hot-water soluble removable material 300 dissolves.

The application of the hot-water soluble removable material 300 to thestrip 110 is a last step prior to singulation. The immersion of thepartially singulated strip or the individual units in hot water, or thespraying the partially singulated strip or the individual units with hotwater is a first step after saw singulation.

In another embodiment, the removable material 300 is apolyvinylpyrrolidone polymer, which is a hot-water soluble thermosettingpolymer material that is cured using ultraviolet (UV) light. An exampleof such a polyvinylpyrrolidone polymer is Dymax® UV Curable WaterSoluble Masks 9-20553 Series (Dymax is a trademark of Dymax Corporationof Torrington, Conn.). After the polyvinylpyrrolidone polymer is cured,the strip 110 is singulated. In one embodiment, the strip 110 ispartially sawn, thereby producing a partially singulated strip. Inanother embodiment the strip 110 is sawn through completely, therebysingulating the strip into individual units. After singulation, thepartially singulated strip or the individual units are immersed in hotwater or sprayed with hot water (at about 120-150° F.) until thepolyvinylpyrrolidone polymer dissolves, thereby removing thepolyvinylpyrrolidone polymer from the recess 134, and revealing adebris-free recess.

In another method in accordance with the invention, the removablematerial 300 is polyimide, and the polyimide is removed, using acetone,after singulation, and revealing a recess 134 that is debris-free.

In various other embodiments, the removable material 300 is another typeof polymer, a polymer adhesive, or a photo-resist material, which isthen removed after singulation, and revealing a recess 134 that isdebris-free.

In one embodiment, a partial saw procedure is performed on the strip 110after depositing the removable material 300 to allow for removal of theremovable material 300 while the strip is still in strip form. In suchone embodiment, the strip 110 is partially sawn, which means sawnentirely through the metal lead frame 112 including through theremovable material 300, but not sawn through the mold compound, therebyproducing a partially singulated strip. In such one embodiment, theremovable material 300 can be removed from the depressions 130 of thepartially singulated strip without debris remaining in the recesses 134because the metal lead frame 112 has already been cut through andbecause a primary cause for debris is from cutting of the metal leadframe. The partial saw procedure may use a blade that is slightly widerthan a blade used for a through cut to ensure that the metal lead 120 isnot accidently “clipped” when full singulation is completed afterremoving the removable material 300. In another embodiment the strip 110is sawn through completely, thereby singulating the strip into fullysingulated individual units.

In each embodiment of the second method, the strip 110 is singulated orpartially singulated after the removable material 300 is placed in thedepressions 130 and only while the removable material is in thedepressions. In each embodiment of the second method, after the strip110 is singulated or partially singulated, the removable material 300 isremoved.

FIG. 11 is a partial, side-elevational view illustrating the manner inwhich the package 140 assembled in accordance with one of variousembodiments of the invention, is mounted to the PCB 152, and showing asolder fillet 1100. The methods (see FIGS. 18 and 19) and the package140 produced thereby in accordance with various embodiments of theinvention aid in the formation of a well-formed solder fillet that canbe easily inspected visually.

FIG. 12 is a top isometric view of a quad, flat-pack no-lead package 140that was manufactured, or assembled, utilizing the second method (seeFIG. 19) in accordance with the invention, in which a strip similar tostrip 110 was singulated while the removable material 300 was disposedin the depressions 130. The removable material 300 was removed aftersingulation, and, as illustrated in FIG. 12, there is a debris-freerecess 134 at an external corner of each lead 120.

FIG. 13 is a bottom plan view of the package 140.

FIG. 14 is a perspective view of an enlargement of an encircled regionshown in FIG. 13 showing several debris-free recesses 134 in accordancewith the invention.

FIG. 15 is a perspective view of an enlargement an encircled regionshown in FIG. 14 showing one debris-free recess 134 in accordance withthe invention. The second method (see FIG. 19), and the package 140produced thereby, results in the debris-free recess 134 shown in FIG.15.

FIG. 16 is a perspective view of an enlargement of a prior art recess1634 showing debris 1635 in the prior art recess.

FIG. 17 is a partial, side-elevational view illustration the manner inwhich a prior art semiconductor package, which includes a prior art body1742 and the prior art recess 1634 in a prior art lead 1620, is mountedto a PCB 1752, and shows how formation of a prior art solder fillet 1700is adversely affected by the debris 1635 in the prior art recess.

FIG. 18 is a flow diagram of a first method of assembling the package140 in accordance with an embodiment of the invention that utilizes thewettable material 200. The first method starts with a standard strip 110that has standard depressions 130 in the lead frames 112, whichdepressions are used for creating recesses 134 after singulation. Thefirst method performs standard package assembly up to and including astep of encapsulation of the strip 110 with mold compound. Next, thedepressions 130 are filled with the wettable material 200. Next, thestrip 110 is heated so that wettable material 200 reflows, and then, thestrip is allowed to cool to room temperature. Next, the strip 110 issingulated. Advantageously, the strip 110 is singulated in a standardway with saw standard blades and techniques, notwithstanding thepresence of the wettable material 200 in the depressions 130. Next,normal assembly is resumed. An end of the first method results incomplete package assembly with solder in the recesses 134 of a completedpackage 140.

FIG. 19 is a flow diagram of a second method of assembling the package140 in accordance with an embodiment of the invention that utilizes theremovable material 300. The second method starts with a standard strip110 that has standard depressions 130 in the lead frames 112, whichdepressions are used for creating recesses 134 after singulation. Thesecond method performs standard package assembly up to and including astep of encapsulation of the strip 110 with mold compound. Next, thedepressions 130 are filled with the removable material 300 such as bydipping the strip 110 into in a tank or reservoir of the removablematerial, or by curtain coating the strip with the removable material,or by stencil printing. Next, the removable material 300 is cured perrecommendation of manufacturer of the removable material to make theremovable material hard and/or stiff. Next, the strip 110 is singulatedusing standard singulation techniques, or partial saw singulation isperformed on the strip. Advantageously, the strip 110 is singulated in astandard way with saw standard blades and techniques, notwithstandingthe presence of the cured removable material 300 in the depressions 130.Next, the removable material 300 is rinsed or removed from thesingulated lead frames 112. Next, normal assembly is resumed. An end ofthe second method results in a completed package 140 having debris-freerecesses 134.

In some embodiments, the depressions 130 are filled with the material400 after the strip 110 is molded because at this stage, there is verylittle likelihood of contaminating other portions of the after the stripis molded. By moving wettable material 200 into the depressions 130after the strip 110 is molded, there is little chance of the wettablematerial running down inside the lead frames 112 and contaminating wirebonds, die surfaces or die flag attach areas because they are alreadyprotected by the molding process. In other embodiments, the depressions130 are filled at any stage of assembly prior to singulation.

It has been determined by experimentation that the lead frames 112 canbe saw singulated cleanly by proper management of blade loading withoutmelting the material 400 that is disposed within the depressions 130.

FIG. 20 is an illustration of one example of a strip such as strip 110,which may be used in one or more methods of assembling packages 140 inaccordance with various embodiments of the invention. The stripillustrated in FIG. 20 includes three arrays of lead frames, each arrayincluding twenty-five lead frames such as lead frame 112, for a total ofseventy-five lead frames.

In one embodiment, the package 140 is a quad, flat-pack no-lead (QFN)package (hereinafter “QFN-style package”). Examples of QFN-stylepackages are: a power quad flat-pack no-lead (PQFN) package, anextremely-thin quad flat-pack no-lead (XQFN) package, a depopulatedvery-thin quad flat-pack no-lead (DQFN) package, and a heatsinkvery-thin quad flat-pack no-lead (HVQFN) package. QFN-style packages mayalso include other types of flat-pack no-lead packages. In anotherembodiment, the package 140 is a dual flat-pack no-lead (DFN) package.

Although a person of skill in the art will note that FIGS. 1 and 4illustrate a strip used in assembling a dual flat-pack no-lead typepackage, and that FIGS. 7-9 and 12-14 illustrate a quad flat-packno-lead type package, for ease of description, these will be treated asshowing a same product, because the method in accordance with thepresent invention is applicable equally to both quad and dual flat-packno-lead type packages.

The specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of the present invention. Any benefits,advantages or solutions to problems described herein with regard tospecific embodiments are not intended to be construed as a critical,required or essential feature or element of any or all the claims.Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements. Note that the term “couple” has beenused to denote that one or more additional elements may be interposedbetween two elements that are coupled.

The Detailed Description section, and not the Abstract section, isintended to be used to interpret the claims. The Abstract section mayset forth one or more but not all embodiments of the invention, and theAbstract section is not intended to limit the invention or the claims inany way.

Although the invention is described herein with reference to specificembodiments, various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below.

What is claimed is:
 1. A method of manufacture, comprising: providinglead frame strip that includes a plurality of lead frames each of whichincludes: an outer frame structure defining a central opening, a die paddisposed within the central opening, and a plurality of leads attachedto the outer frame structure and extending inward toward the die pad inspaced relation to each other, wherein each lead of one lead frameextends outward from its die pad and is integral with a lead thatextends outward from a die pad of an adjacent lead frame; creating anelongated depression in the lead frame strip, the elongated depressionhaving a middle portion and two end portions, each of the two endportions becoming, after singulating of the lead frame strip intoindividual lead frames, a recess at a corner of an end of a lead; andfilling the elongated depression with a material prior to singulating ofthe lead frame strip into individual lead frames.
 2. The method ofmanufacture of claim 1, including a step of encapsulating the lead framestrip with a mold compound.
 3. The method of manufacture of claim 1,including a step of singulating the lead frame strip into individuallead frames.
 4. The method of manufacture of claim 3, wherein thematerial is a solder wettable material.
 5. The method of manufacture ofclaim 3, including a step of removing the material from the individuallead frames after the step of singulating.
 6. The method of manufactureof claim 4, wherein the material remains in the elongated depressionafter the step of singulating.
 7. The method of manufacture of claim 1,in which the material is a material from a group consisting of: anadhesive material, a thermoplastic material and a polymer material. 8.The method of manufacture of claim 1, wherein the material is soluble inwater that is above room temperature.
 9. The method of manufacture ofclaim 8, in which the material is a thermosetting polymer material. 10.The method of manufacture of claim 1, in which the material ispolyimide, and including a step of removing the polyimide, usingacetone, after the step of singulating.